1. Field of the Invention
The present invention relates to an ink cartridge having an ink chamber filled with ink and a storage chamber containing a porous member impregnated with ink. In particular, the invention relates to improvements in the ink passage between the ink chamber and the storage chamber.
2. Description of Related Art
In an ideal ink cartridge of this type, the ink in the storage chamber is first consumed through the ink passage and the ink chamber. Then, air is supplied from the storage chamber to the ink chamber, while ink in the ink chamber is consumed. The cartridge is connected to a recording head mounted on the carriage of a printer. Because the carriage reciprocates at high speed, the air in an upper portion of the ink chamber is formed into bubbles, which are liable to mix with the ink in this chamber. If air mixes with the ink, the recording performance of the printer lowers.
It is preferable that the porous member be fitted in close contact with the inner surfaces of the storage chamber without gaps. Actually, however, gaps or spaces remain along edges of the storage chamber around the porous member. The gaps are liable to be air passages.
Japanese Patent Laid-Open Publication No. H.6-238908 discloses a conventional ink cartridge in practical use for supplying ink to a recording head of an ink jet recorder. The cartridge includes a case partitioned into a liquid chamber and a storage chamber by a partition formed therebetween. The liquid chamber contains ink, and the storage chamber contains a porous member impregnated with ink. The liquid chamber has an ink supply hole, through which ink can be supplied to the head. The storage chamber has an air vent formed through its top wall. The partition between the chambers has a short ink passage formed through it at a predetermined height from its bottom. The passage is fitted with a filter on its side adjacent to the storage chamber. The filter can remove fine foreign substances produced mainly from the porous member.
The size, the shape, the position, etc. of the ink passage in this cartridge are neither disclosed nor suggested to prevent air from flowing from the storage chamber through the passage into the liquid chamber. The ink being sucked from the porous member into the liquid chamber is resisted higher than the air being sucked through the gaps along edges of the storage chamber, and through the passage into the liquid chamber. Therefore, if the passage is wide, air is liable to flow into the liquid chamber when ink in the cartridge is consumed and negative pressure develops in the liquid chamber. As a result, the ink in the porous member is difficult to supply to the liquid chamber. This lowers the ink consumption rate (ink consumption/amount of filled ink) of the cartridge. Besides, air may mix with the ink in the liquid chamber, thereby lowering the recording performance of the recording head. In particular, when the filter is clogged, and/or when the ink viscosity resistance is high at low temperature, the negative pressure in the liquid chamber may be high. If the negative pressure is high, a remarkable amount of air may flow into the liquid chamber.
Japanese Patent Laid-Open Publication No. H.6-255122 discloses another ink cartridge for supplying ink to a recording head of an ink jet recorder. The cartridge includes a case partitioned into a main ink storage chamber and an auxiliary ink storage chamber by a partition formed therebetween. The main chamber contains ink, and the auxiliary chamber contains a porous member impregnated with ink. The main chamber has an ink supply hole formed through its bottom wall. The auxiliary chamber has an air vent formed through its top wall. The partition between the chambers has an ink passage formed through its bottom. The passage connects the chambers and is fitted with a filter.
When ink is supplied from the main ink storage chamber of this cartridge through the supply hole to the recording head, some negative pressure develops in this chamber. In the meantime, ink is supplied from the porous member in the auxiliary chamber through the passage to the main chamber, and air is introduced through the vent into the auxiliary chamber. While ink is flowing through the fine porous passages in the porous member, the ink is subjected to viscous (viscosity) resistance, capillary (capillarity) resistance, etc. If foreign substances stick to the filter, they resist the ink flowing through it. As a result, the negative pressure develops in the main chamber.
For the size, the shape, the position, etc. of the ink passage in this cartridge as well, nothing is disclosed to prevent air from flowing through the passage into the main ink storage chamber. In addition, the passage is positioned at the bottom of the partition, and extends nearly over the whole width of the auxiliary chamber. Therefore, air which has entered the gaps along edges of the auxiliary chamber flows easily into the main chamber. This prevents the ink in this cartridge, too, from being consumed ideally, thus lowering the ink consumption rate of the cartridge. The recording performance of the recording head is lowered by air mixing with the ink in the main chamber.
The inventors made an experiment with an ink cartridge of the type mentioned first. The experiment has proved that, if the distance between the ink passage and each of the edges of the storage chamber is too short, air is liable to flow from the gaps along edges into the passage. In addition, if the ink chamber is excessively large in comparison with the storage chamber, air is liable to mix with the ink in the ink chamber. This is not preferable in terms of recording performance.